The subject matter disclosed herein relates to a hub flow path contour at an interface between an exit of a turbine and an entrance of a diffuser.
In turbines, high energy fluids flow along pathways where they interact with turbine buckets arrayed at varying turbine stages to produce rotation of the turbine buckets about a rotor and mechanical energy. The fluids eventually exit the pathway and enter a diffuser, which is disposed downstream from the last turbine stage. The diffuser serves to condition the flow of the fluids, which are then directed toward additional equipment disposed downstream from the diffuser, such as a heat recovery steam generator (HRSG).
The trend for modern gas turbines, in particular, has been toward increasing exhaust energy and velocities of the fluids. This is largely a result of the demand for increased power output through increased mass flow but the material and mechanical restrictions of the turbine buckets of the last turbine stage often dictate that the turbine exit annulus area may not be able to grow commensurate with the required increase in mass flow associated with the demand. In order to make up the difference, then, it is frequently necessary to increase a turbine exhaust kinetic energy that will reduce gas turbine efficiency unless the kinetic energy can be recovered in the diffuser. A larger area ratio diffuser will allow more of the kinetic energy to be recovered but also will reduce an operability range, which is defined as a region in which the diffuser is well behaved.
When the diffuser is not well behaved, non-uniform flows of the fluids moving toward the downstream equipments pose a risk of damage to that equipment. For example, where the equipment is an HRSG, non-uniform fluid flow leads to vibration and deterioration of the HRSG.